A grinder of this type is disclosed in French patent No. 91 09788. In this grinder, the active plane of the knife forms an angle of approximately -45.degree. with the radial plane containing the edge of the knife, and the layer of material is, in certain cases, detached from the track in the form of agglomerates. This has drawbacks, particularly when it is desired to dry the material with a hot gas.
The object of the present invention is to ensure the breaking up of the layer of material by the knife and its dispersal, which makes it possible to improve heat exchanges, when the material has to be dried using hot gases, and, if applicable, to facilitate grain size selection, thus permitting selective forward feeding of the material. Another object of the invention is to reduce the wear of the knife and of the deflecting blade.